On 04.03.17 12:29, Jon Elson wrote: > On 03/04/2017 12:02 PM, Gene Heskett wrote: > > Hexfets can be hard to deal with. Bear in mind they are generally shipped > > with a fine wire wrapped around all 3 legs > > I have never received a transistor with wire around it. I > have purchased roughly 3000 FET power transistors for Pico > Systems production.
Nor down here, closer to the penguins. But 100 off 2N7000 small MOSFETs came last month on metallised cardboard strip, the IRLZ44s came in anti-static plastic tubing, and years ago a solid handful of MOSFETs came in a black conductive plastic bag with big yellow ESD handling warning. > The capacitance of a power transistor's gate is so huge it greatly > mitigates the ESD susceptibility. Hadn't thought of that ... sounds good vs the 30 pF of human body capacitance ... but even at 3 nF, that's 10v/kv on 30 pF, so even 20 kv from crossing carpet in dry air becomes 200v = dead MOSFET. I think I'll stick with suppliers who adhere to established antistatic norms, thanks. Back at Siemens, we weren't allowed into the PCB assembly area without conductive shoe-shorting straps, and even then were confined between painted yellow lines bracketing the aisles, out of reach of trouble. (And that wasn't just for engineers - other visitors received the same treatment. ;-) > But, I'm pretty sure the servo amps in these older machines > were bipolar junction transistors. However, after a fault > that blew a fuse, it is quite likely the base drive > circuitry may also be damaged. When I get FETs blown out, I > don't even TEST the gate driver, I just replace it every > time. I think at least the base drive circuits should be > checked. It's well worth that to avoid having to pull it apart again - after having ruined a valuable workpiece. Apropos that, ESD damage can be latent - the device continues to function for a while, then dies later, just like the stressed gate driver, above. I wouldn't install MOSFETs which had not received proper ESD-safe handling from manufacturer to board. Erik (Who experienced the abrupt suicidal tendencies of NMOS devices on mild ESD exposure in the early '70s. Thank the pixies that MOS is somewhat more robust now.) ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
